Securing elements of the aforesaid type are supported through the retaining tongues by positive engagement and force-locking on the surface of a shaft. The securing elements also designated as indented rings in DE 33 05 419 A1 are resilient and hardened. The radial dimensions of the clear cross-section of a hole between the retaining tongues (teeth) situated opposite each other at the central axis of the indented ring are smaller than the outer radial dimensions of the shaft measured in the same direction on the seat of the indented ring. When the indented ring is pushed onto the shaft, the teeth deflect elastically and yield outwards so that the free cross-section of the hole is enlarged to the outer radial dimensions of the shaft and the shaft can be pushed into the hole.
The front edges of the retaining tongues dig themselves slightly into the surface of the shaft at the desired position of the indented ring under the resilient pre-stress exerted by the retaining tongues. For this purpose, the shaft must have a soft surface. The front edges cut themselves into the material on the surface of the shaft. The seat of an indented ring is therefore formed as a rule by positive engagement and force-locking. When the indented ring is loaded in a direction opposite the original insertion direction of the shaft, the indented ring is supported through the retaining tongues on the shaft and digs itself into this. Such securing elements are therefore designated as self-locking securing elements.
Advantageously, securing elements of this type can be fixed on shafts at any desired points irrespective of the tolerances. In addition, these securing elements can be manufactured economically as mass articles and are preferably used, for example, in the upper part of steering columns for assuring the shaft seating of steering bearings on the steering shaft.
A steering column of the generic type is described in EP 2 249 050 A1. The steering bearings are angular contact ball bearings. The inner rings of two angular contact ball bearings positioned against each other and pre-stressed against each other are centered, each one, by a respective clamping ring on the shaft. A wavy spring or another spring is elastically biased in axial direction against each of the clamping rings. The spring, the clamping ring and thus also the respective inner ring is fixed in place through an indented ring.
A steering bearing of the generic type for a rotatable mounting of a shaft configured as a steering spindle in a steering column tube is described in DE 10 2009 051 107 B3. The inner ring of the angular contact ball bearing is configured integrally with the generic securing element. Advantageously, one component less must be mounted during assembly of the steering column. The work and expenditure for the assembly, the feeding, the storage and transportation can be kept at a low level. In addition, manufacturing costs of such steering columns are also reduced.
Steering columns are sub-assemblies of which high demands are made with respect to safety of operation and behavior during a crash. For example, a dagger-like penetration of the steering spindle into the driver's cab during a crash must be absolutely excluded. The requirements made of the axial retaining ability of the generic securing elements are therefore very high.
Indented rings and inner rings of steering bearings with integrated securing elements are punched out of sheet metal and cold shaped. The front edges are the result of the initial punching of the mostly rotationally symmetric rings. Not least of all, the retaining ability of the securing elements depends on the configuration of the front edges.
Edges are usually formed by two converging surfaces. One of these surfaces that end at the front edge is accordingly the front end surface of the retaining tongues that extends cross-wise to both the front surfaces of the retaining tongues and is directed towards the central axis. This front end surface is created during the manufacture of the securing element by punching and defines a part of the hole in the securing element in radial direction. The other surface is a planar section on a front side of the securing element of the respective retaining tongue and is directed in direction of the shaft during the mounting of the indented ring in feeding direction.